It is known that a table tennis paddle usually comprises a striking head, which is generally flat with a rounded contour, for striking the ball, said striking head being attached to a handle by which the user holds the instrument. Typically, the head comprises a core, known as the blade, formed of a sheet of rigid material, such as wood in top-of-the-range paddles. The blade is covered, on at least one side and generally on both sides, with an elastomeric coating, commonly called a “sole”, the entire surface of which is lined with pimples which are formed integrally in the material of the coating and generally have a stem which protrudes transversely from one of the faces of the coating.
According to a conventional embodiment, the face coated with pimples is arranged on the outer side of the blade and makes direct contact with the ball. The pimples which come into contact with the ball flex elastically under the impact and deaden the impact in order to give the player better control when hitting the ball. In addition, these pimples store energy by deforming under impact and impart an additional driving force to the ball being returned as they regain their shape.
According to another embodiment, which is also conventional, but reserved more for top-of-the-range paddles, the pimples of the coating are directed towards the blade. The outer face of the head of the paddle, which is intended to come into contact with the ball, consists of the face of the coating or of the sole opposite the pimples. It has an essentially smooth appearance to the naked eye. Between the face covered with pimples and the rigid sheet forming the blade is inserted a layer of elastic material having a low modulus of elasticity, generally made of elastomer foam, to which the coating is joined by adhesive bonding.
Traditionally, the pimples formed integrally in the material of the coating are cylindrical. The body of the cylindrical pimple is attached to the solid sheet in two different ways. The attachment is either formed by a sharp-angled profile (as seen in section), in which the generator of the cylinder forms an angle of 90° with the planar surface of the coating from which the pimple emanates; or this attachment is carried out by softening this angle by deburring or by way of a small truncated fillet.
Whatever the configuration adopted, the essential function of the pimples is to confer “rebound” on the ball by deforming under the impact in order to help to drive it back. By way of their lateral deformation, they are also involved in improving the lateral interactions between the ball and the paddle and in increasing their tangential grip in order to enable the player to impart spin to the ball and to precisely control the return direction he/she wishes it to have. It can also be seen that the work of the pimples results in long-term wear and fatigue of the material. Furthermore, in the case of powerful forces, buckling phenomena of the wall of the material are observed at certain points on the sole. These phenomena are liable to lead to the formation and propagation of splits in this material, which ultimately reduce the efficiency of the paddle until it is unsuitable for use.
The prior art shows that attempts have been made to improve the performance of paddles by modifying the shape of the pimples. Thus, Japanese Patent Application JP2004113568A illustrates pimples having a truncated conical shape, in which the diameter of the pimple decreases between its plane of attachment to the surface of the coating and its free end. In one embodiment illustrated in said document, the shape is interrupted half way up the pimple, from which point the profile becomes cylindrical as far as thefree end face of the pimple. A pimple having a similar profile is also shown in the drawing of document DE102006034795 A1.
However, tests carried out by the applicant with shapes having a truncated conical attachment profile, which is for example inclined at 45° between the pimple and the planar surface of the coating, show that these arrangements have only limited success in reducing the above mentioned difficulties and improving the durability of the paddle with respect to conventional designs. Furthermore, beyond these deficiencies, there exists a demand on the part of the players, in particular professional sportsmen and -women, for an improvement in performance, in particular in terms of the grip between the face of the paddle and the ball at the moment of impact and until the ball is returned, and also for a decrease or even elimination of the inconsistencies in the behaviour of the paddle which result from the appearance of non-linear phenomena such as buckling of the pimples.
Also cited for the record is utility model CN2442706 (Y), in which perfectly cylindrical pimples have a concave end face intended to modify the point contact of the pimple with the ball. However, this arrangement does not appear to have any effect on the behaviour in terms of flexibility and endurance of the body of the pimple. Document to EP1683552 is directed at a table tennis paddle coating, in which the surface which comes into contact with the ball, rather than having pimples, is lined with adjacent cavities, wherein the properties of flexibility and contact with the ball go in the opposite direction to those which can be found with the aid of pimples.